Historical:Upper Devonian Series
Charles Collinson and Elwood Atherton
The term "Upper Devonian Series" has been in general use in Illinois since 1925 (Bassett).
Prior to 1925 the New York terms "Senecan" and "Chautauquan" had been used in addition to Upper Devonian (figs. D-4, D-5).
Extent and Thickness
Upper Devonian sediments underlie most of southern and western Illinois. They completely overlap the then subsiding Sangamon Arch, on which Middle Devonian sediments had not been deposited (fig. D-18). They are more than 300 feet thick in Hardin County and as much as 275 feet thick in Mercer County, but elsewhere they are generally less than 200 feet.
In the Devonian type region in England, Upper Devonian applies to the Frasnian (lower) and Famenian (upper) Stages. Conodont studies by Collinson (1967) placed the base of the Frasnian at the base of the Sylamore Sandstone in central and western Illinois, at the top of the Alto Formation in southwestern Illinois, and a few feet below the top of the Blocher Shale in southeastern Illinois. Savage (1920) included the Alto and younger Devonian rocks in the Upper Devonian, as did Weller (1940), Cooper et al. (1942), Cooper (1944), and Orr (1964). However, Weller (1944b), on sedimentational evidence, and Collinson et al. (1967a), on the basis of conodont faunas, tentatively placed the Alto in the Middle Devonian, which is the current practice. The position of the top of the Upper Devonian Series was long debated, as described under the discussion of the Devonian System, but the top of the Louisiana Limestone (or a few feet above it in the Hannibal Shale) in western Illinois, the top of the Grassy Creek Shale in southwestern Illinois, and a position near the top of the New Albany Group in eastern Illinois are now generally accepted as the top of the Upper Devonian.
The Upper Devonian rocks are generally conformable on the Middle Devonian strata, but in western and southwestern Illinois a minor unconformity occurs at the base of the Sylamore Sandstone, of the Sweetland Creek Shale, or of the Grassy Creek Shale.
In the major part of the Illinois Basin the Upper Devonian Series consists largely of the black and gray shale of the New Albany Group, but on the flanks of the Ozark Uplift and on the Mississippi River Arch it also includes limestone, sandstone, and siltstone (fig. D-19).
The Louisiana Limestone contains a large variety of macrofossils (Williams, 1943), but the shales generally contain few. Zonation in the series, therefore, is based largely on the conodonts, which, along with abundant Tasmanites, are common in the shale formations.
BASSETT, C. F. , 1925, Devonian strata of the Alto Pass Quadrangle: Illinois Academy of Science Transactions, v. 18, p. 360-368.
COLLINSON, CHARLES, 1967, Devonian of the north-central region, United States, in International symposium on the Devonian System: Alberta Society of Petroleum Geologists, v. 1, p. 933-939; Illinois State Geological Survey Reprint 1968-G.
COLLINSON, CHARLES, L. E. BECKER, G. W. JAMES, J. W. KOENIG, and D. H. SWANN, 1967a, Illinois Basin, in International symposium on the Devonian System: Alberta Society of Petroleum Geologists, v. 1, p. 940-962; Illinois State Geological Survey Reprint 1968-G.
COOPER, G. A., 1944, Remarks on correlation of Devonian formations in Illinois and adjacent states: Illinois State Geological Survey Bulletin 68, p. 217-222.
COOPER, G. A., et al., 1942, Correlation of the Devonian sedimentary formations of North America: Geological Society of America Bulletin, v. 53, p. 1729-1794.
ORR, R. W., 1964, Conodonts from the Devonian Lingle and Alto Formations of southern Illinois: Illinois State Geological Survey Circular 361, 28 p.
SAVAGE, T. E., 1920, Devonian formations of Illinois: American Journal of Science, v. 49, p. 169-182.
WELLER, J. M., 1940, Geology and oil possibilities of extreme southern Illinois: Illinois State Geological Survey Report of Investigations 71, 71 p.
WELLER, J. M., 1944b, Devonian correlations in Illinois and surrounding states-a summary: Illinois State Geological Survey Bulletin 68, p. 205-213.
WILLIAMS, J. S., 1943, Stratigraphy and fauna of the Louisiana Limestone of Missouri: USGS Professional Paper 203, 133 p.
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